Beyond 3D, 4D Printed Adaptive Devices

Researchers are, at least from an engineering perspective, right now breaking the fourth wall. Combining photo-responsive fibres with thermo-responsive gels they’ve developed a new hybrid material that could be able to reconfigure itself into different shapes, time after time, when exposed to light and heat. This could allow for the creation of devices that can display different behaviour when acted on by specific outside forces, therefore become amazingly adaptable to their environments.

‘In 4D printing, time is the fourth dimension that characterises the structure of the material; namely, these materials can change shape even after they have been printed. The ability of a material to morph into a new shape alleviates the need to build a new part for every new application, and hence, can lead to significant cost savings,’ explains Dr. Anna Balazs, Professor of Chemical and Petroleum Engineering at the University of Pittsburgh’s Swanson School of Engineering, ‘The challenge that researchers have faced is creating a material that is both strong and malleable and displays different behaviour when exposed to more than one stimulus.’

And it looks like they’ve found the solution. By embedding light-responsive fibres, which are coated with spirobenzopyran – or SP – chromophores, into a temperature-sensitive gel the new material begins to exhibit very different behaviour when exposed to light than with heat. Computer models developed by Dr. Balazs and Dr. Olga Kuksenok, Associate Professor of Materials Science and Engineering at Clemson, show that these composites would be both highly reconfigurable and mechanically strong, thus showing a potential for biomimetic four-dimensional printing.

When this new material is fixed to a surface, it bends one way under a light source and another way when heated. Furthermore, when it’s unattached it shrinks up on itself, collapsing like an accordion with heat, yet under light it curls up in a spiral. This shows programmable behaviour, meaning that this single object can adopt different shapes, and therefore functions, depending on what is stimulating it. This could have terrific applications, especially in robotics where biomimetic, stimulation-responsive motion could be used to make joints that bend and unbend with light.

‘Robots are wonderful tools, but when you need something to examine a delicate structure, such as inside the human body, you want a “squishy” robot rather than the typical devices we think of with interlocking gears and sharp edges,’ Dr. Balazs said, ‘This composite material could pave the way for soft, reconfigurable devices that display programmed functions when exposed to different environmental cues.’

However, she goes on to say, ‘The real significance of the work is that we designed a single composite that yields access to a range of dynamic responses and structures. On a conceptual level, our results provide guidelines for combining different types of stimuli-responsive components to create adaptive materials that can be controllably and repeatedly actuated to display new dynamic behaviour and large-scale motion.’

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